Seahorses are named for their equine appearance with bent necks and long snouted heads followed by their distinctive trunk and tail. Although they are bony fish, they do not have scales. Instead, they have a thin skin stretched over a series of bony plates. These bony plates are arranged in rings throughout their bodies. Each species has a distinct number of rings. Seahorses swim upright, another characteristic not shared by their close pipefish relatives, which swim horizontally. Seahorse is the name given to the 54 species of small marine fishes in the genus Hippocampus. “Hippocampus” comes from the Ancient Greek word hippos meaning “horse” and kampos meaning “sea monster”, though these docile species are a far-cry from monsters.

Seahorses range in size from 1.5 to 35.5 cm (0.6 to 14.0 in).

Seahorses swim very poorly. They flutter a dorsal fin and use pectoral fins (located behind their eyes) to steer. Their rapid fluttering of the dorsal fin is reminiscent of a hummingbird in flight. Seahorses have no caudal fin. Since they are poor swimmers, they are most likely to be found resting with their tails wound around a stationary object, referred to as hitching. They have long snouts, which they use to suck up food. Like a chameleon, their eyes can move independently of each other. Also, like a chameleon, seahorse are masters of camouflage. The can readily change their color to adapt to their surroundings.